Specimen thickness effects on Mode I and Mode II interlaminar toughness of composites using finite element analysis

Laminated fibre-reinforced polymer composites are highly susceptible to delamination damage. Their delamination resistance, characterized by the interlaminar fracture toughness (IFT), is of major concern. Owing to orthotropy, it is believed that pure Mode I, as well as pure Mode II interlaminar failures are possible. Experimental measurement of Mode I IFT has been standardized through DCB specimen. For Mode II testing, ENF specimen is widely used. Nonetheless, controversies amongst various test configurations to obtain the representative values stall the standardization of Mode II IFT test.

The present focus is to investigate specimen thickness effects on IFT values through finite element analysis of 2-dimensional linear elastic models of composite DCB and ENF specimens. Our results conclude thickness independence for both the specimens. Such evidence is significant towards the development of an acceptable Mode II IFT test standard. However, various unaccounted corrections may mischievously manifest as distinguishable thickness/other geometry effects.